The present invention relates to a sheet supply device for supplying a sheet and an image forming apparatus having the sheet supply device.
In a conventional image forming apparatus such as a printer, a copier, a facsimile, and the likes, a sheet supply device is provided for supplying a sheet to an image forming unit for forming an image on the sheet.
When the sheet supply device is a retard separation type as a sheet separation type, a separation supply unit is disposed on a sheet pick up side of a medium tray storing a medium for separating and supplying the medium one by one. The separation supply unit includes a retard separation unit for separating the medium thus picked up. The retard separation unit includes a sheet supply roller to be pressed against the medium for picking up the medium; a transportation roller; and a separation roller abutting against the transportation roller.
The separation roller of the retard separation unit generates torque in a direction of returning the medium backward. When only one medium is supplied, the separation roller follows and rotates in a sheet supply direction through friction between the medium and the separation roller. When more than two media are supplied, the separation roller generates a medium separation function and applies brake to the media with the torque, thereby supplying only one medium.
In Patent Reference, a double supply regulating unit (a primary separation unit) is separately disposed between a sheet supply roller and a retard separation unit (a secondary separation unit). The double supply regulating unit (the primary separation unit) separates a leading edge of a medium picked up with the sheet supply roller. The retard separation unit (the secondary separation unit) includes a guide member for guiding the medium, and has a function of preventing a plurality of media from being supplied to the retard separation unit.    Patent Reference: Japan Patent Publication No. 2006-248689
In an electro-photography printer as an image forming apparatus, there has been a demand for reducing energy consumption and a space, thereby making it necessary to reduce a size of the electro-photography printer. On the other hand, it is necessary to print on various types of media according to various applications. Accordingly, it is necessary to improve a function capable of transporting various types of media.
In particular, in an electro-photography printer capable of printing a color image, it is necessary to print on a medium having a large thickness. When the sheet supply device disclosed in Patent Reference supplies a medium having a large thickness, however, the primary separation unit may be excessively deformed due to stiffness of the medium, so that the primary separation unit thus deformed interferes with the secondary separation unit disposed on a downstream side in a medium transportation direction.
To this end, rigidity of the primary separation unit may be increased. Alternatively, the primary separation unit may be disposed sway from the secondary separation unit, so that the primary separation unit can stably separate the medium without interfering with the secondary separation unit even when the primary separation unit is deformed. However, when the primary separation unit is disposed sway from the secondary separation unit, it is necessary to increase a size of the image forming apparatus.
In view of the problems described above, an object of the present invention is to provide a sheet supply device and an image forming apparatus capable of solving the problems. In the invention, it is possible to stably separate a medium without interfering with a secondary separation unit even when a primary separation unit is excessively deformed due to stiffness of the medium.
Further objects of the invention will be apparent from the following description of the invention.